Your output voltage should be adjustable around .1vrms, this will produce a good result in your vaping experience, and also look for a product which has battery readout option, this particular option gives the user the option of fully utilizing the overall life of the electronic cigarette battery. Check the power efficiency on the product, a good product has more than 98% power efficiency and is compatible with imr batteries; this will give you many alternatives when buying accessories. Some products have chargers which are compatible with lithium ion 3.7volt configuration. Good products also have a standby mode where the battery consumption is less than .3ua. One that comes to mind is this one: http://vapingproducts.topvapes.org/best-vaporizers/volcano-review

A good product will have user storage setting, it is a great feature, safety features are also important, look for a product which has a lock mode, this will prevent accidental triggering and will save battery and you’re E-liquid. Short circuit protection is also a good feature and many products offer this benefit nowadays, with most products there is a 10-12 second safety timeout, i-e if you stop puffing your electronic cigarette for more than 10-12 seconds, it will automatically turn off, some electronic cigarettes even offer adjustable timeout options, you can set the timer for as high as 30-45 seconds depending on your mood. In the end it is all about the quality of smoke but one must agree that these benefits fo increase smoking pleasure and convenience.